Linux: Stopping Virtual Camera Requires v4l2loopback Restart to Restart Virtual Camera

Operating System Info

Ubuntu 24.04

Other OS

No response

OBS Studio Version

31.1.2

OBS Studio Version (Other)

No response

OBS Studio Log URL

https://obsproject.com/logs/QzOiXzO43puQU00c

OBS Studio Crash Log URL

No response

Expected Behavior

After stopping the virtual camera, it should restart without issue.

Current Behavior

The virtual camera fails to start, showing the following error:

Steps to Reproduce

1. Start the virtual camera after a fresh boot with v4l2loopback up and running.
2. Stop the virtual camera.
3. Start it again.
   ...

Anything else we should know?

This started for me with 31.1.0.

As shown in the logs, after stopping v4l2loopback, /dev/video has the following:

crw-rw----+ 1 root video 81, 1 Aug 14 06:01 /dev/video0
crw-rw----+ 1 root video 81, 2 Aug 14 06:01 /dev/video1
crw-rw----+ 1 root video 81, 0 Aug 14 18:43 /dev/video10

modprobe --remove v4l2loopback results in /dev/video10 going away.
modprobe v4l2loopback (reloading it) brings /dev/video10 back.

Let me know if there's any other information (such as the output of lsmod or the kernel module configuration for v4l2loopback) you may need.

Thanks so much!

Start with the linked OBS log and reproduce the listed Linux sequence: start, stop, and restart the virtual camera while v4l2loopback is loaded. Inspect the virtual-camera start and stop entry points involved in the failure, using the /dev/video10 and modprobe behavior as clues. Done means the camera restarts without requiring a v4l2loopback module reload.